Researchers learn about gas-giant cores by hammering diamond with lasers

The National Ignition Facility does more than fusion.

The discovery of so many exoplanets in recent years has raised many new questions, forcing us to reexamine some of our ideas. Scientists had extrapolated models of stellar system evolution from our own Solar System, assuming that others look very similar to our own. But extrapolation can only get us so far. Scientists never expected to find so many “hot Jupiters”—gas giants larger than Jupiter and orbiting very close to their star.

We’re also having a hard time understanding the inner workings of exoplanets and stars with much greater mass than Earth. Scientists have managed to test some materials under extreme pressures and found that our conventional ideas about a material’s behavior may not apply. Certain exotic quantum mechanical models could apply in such extreme cases, but until recently, scientists have not been able to test those models’ predictions.

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The difficulty, of course, is that actually visiting the cores of gas giants to test our understandings is wildly impractical. The next best thing, then, is to recreate these massive pressures on Earth and study their effects on materials. As impossible a task as it may seem, scientists at the National Ignition Facility (NIF) used its enormous lasers to do exactly that.

The NIF machine is a sight to behold, so exotically futuristic that it recently doubled as the warp core of the Starship Enterprise in last year’s “Star Trek Into Darkness." It's a massive aluminum sphere, 10 meters in diameter, that houses the world’s largest laser. When not acting as a “radioactive catastrophe waiting to happen" as Scotty put it in the film, the NIF is used for nuclear fusion experiments. Luckily, the machine’s resources are also occasionally allocated to fundamental physics research.

Taking advantage of that time, a group of scientists devised an experiment to learn about conditions inside massive exoplanets. To simulate the dense material at the cores of such planets, they used a synthetic diamond. The goal of the experiment was to put massive amounts of pressure on the diamond and to observe how much the diamond compressed.

To do so, the researchers fired 192 laser beams at the crystal over the unimaginably short period of two nanoseconds. This firing created pressures similar to those found at the core of Saturn, approximately 14 times greater than the pressure at the center of the Earth.

This was the first time this method, called dynamic ramped compression, was used successfully. Other approaches are incapable of reaching the incredible pressures seen in this experiment, so the success of ramped compression means we might be able to test even higher pressures. However, ramped compression requires extremely precise control—making NIF perfect for the job, as its laser is capable of incredible precision.

The experiment achieved an almost fourfold compression of the diamond, in the process gaining data that we can now compare to theory. Since the diamond is made of carbon, the team’s data can be used to extrapolate to the cores of planets comprised mostly or entirely of carbon compounds.

Because titanic pressures such as those seen in the team’s experiment are normal in some planets, scientists can use the new data to derive a better mathematical relationship between a carbon planet’s mass and its size. In other words, scientists should be able to more accurately calculate the sizes of carbon-rich exoplanets.

We live in an exciting era—exoplanets are being discovered at an incredible rate (with more found in 2013 than in every prior year put together), and new techniques are enabling scientists to study them with greater precision. Studies like this one, which push the boundaries of what can be tested experimentally on Earth, will be crucial to that endeavor.